Equivalent Circuit and Vector Diagram of an Autotransformer with Mapping of Magnetic Fluxes

A universal equivalent circuit of an autotransformer with explicit mapping of its main characteristic—transporting energy by two parallel paths (electrically and electromagnetically)—is presented. At the same time, a diagram displays the magnetic fluxes in the window sections and in separate sections of the magnetic circuit, as well as when the steel is saturated between it and the tank. A similar completeness of representation of the power and magnetic fluxes is provided by the vector diagram of autotransformer operating mode. With its help, a high degree of clarity was achieved when explaining overexcitation of individual parts of a magnetic circuit in a short-circuited autotransformer and when deriving formulas for determining super- and antisupercurrents in comparison with idle fluxes in this mode. The presented equivalent circuit is suitable for step-up and step-down autotransformers and is applicable to the study the steady-state and transient processes.     

Protection of a Single-Phase Transformer from Interwinding Failure in Windings of Integral Magnetic Transformers

A simple means of protection of a powerful single-phase transformer with integral magnetic transformers has been suggested. The protection has a high sensitivity to the interwinding failure and is based on the measurements of unsymmetry of the leakage magnetic fluxes of transformer windings. This magnetic unsymmetry is determined by the difference of electromotive forces of windings of two magnetic transformers placed symmetrically with respect to the symmetry plane of the protected transformer. It has been suggested to produce the magnetic transformers in the form of a single-layer winding with an alternating pitch, which is wound around a textolite round or rectangular body. The length of a magnetic transformer is taken to be equal to the length of a magnetic core, which allows one to provide independence of protection sensitivity on the location of closed turns on the transformer rod. To measure the difference of the emf of magnetic transformers, the circuit of comparison with a responsive element in the form of a TT-40/0.2 or RT1-P/0.15 current relay has been used. Methods to determine a trigger threshold and sensitivity of the protection to interwinding failure as well as to ironwork failure have been suggested.     

Power Supplies for Electronic High-Voltage Measuring-Current Transformers

A power supply for electronic high-voltage measuring-current transformers with extraction of energy from the measured current that flows through a high-voltage line has been considered. A magnetic core of the supply transformer from the windings of which the necessary power is extracted is mounted on the line for this purpose. When the line current changes over a wide range, the supply transformer should have a quickly saturated magnetic core. It has been shown that, to reduce the losses and decrease the loading of the elements of a power-supply circuit in a wide current range, a ballast load should be introduced in the circuit of a secondary winding. Three variants of the ballast load have been compared: resistive, capacitive, and in the form of a transistor-current limiter. The results of simulations in the VisSim software have been considered for all three variants, as well as for the case of absence of a ballast load in the power-supply circuit. The simulations were carried out for the lowest and highest measured currents, as well as for the line short-circuit mode. The results of simulations have shown the advantages of a power supply based on a saturated transformer with a transistor-current limiter. A variant of a circuit of a transistor-current limiter has been suggested.     

一种新的变压器磁路到电路的转换模型及多种方法的统一

变压器的建模计算方法有两个关键点,一个是磁化曲线的表示,一个是磁路到电路的等值转换模型。针对第二个关键点提出了一种新的转换模型,把铁芯柱、铁轭、漏磁路径都等效成匝数为一次绕组的线圈,利用电流拆解方法表示各线圈的电流关系,利用磁通的连续性表示电动势的关系,从而得到与磁路等值的电路模型。该电路模型与对偶原理法得到的电路模型相同,并且该模型可以得到与统一磁路UMEC法相同的变压器铁芯动态自感和互感值,验证了所提新方法的正确性以及所提方法、对偶原理法、统一磁路UMEC三种方法的统一。最后给出计及变压器饱和特性的电磁仿真计算流程图。     

Specific features of the development of differential-phase transformer protection systems on the basis of magnetic reed switches

It shown that the magnetic reed switches installed close to flexible current leads of power transformers with power over 6.3 (40) MV A and high voltage 10 (35) kV may be used as a basis of phase-comparison circuits with specified boundary angles in the devices for the protection of these transformers against short circuit. The response threshold of these circuits, the errors caused by the differences between the intrinsic response times, inaccuracies in settings of magnetic reed switches, and regulation of the transformer voltage are estimated. A technique for suppressing the effects of adjacent phases and electric installations is presented.     

一种新的三绕组自耦变压器的非线性建模

自耦变压器的精确建模在分析变压器运行于磁饱和区域的特性时至关重要。从单相三绕组自耦变压器的电磁关系入手,推导出折算到高压侧的三绕组自耦变压器的等效电路。给出模型中的线性绕组漏阻抗参数和非线性激磁阻抗参数的计算方法,并详细介绍了利用磁等值回路图得到激磁电抗非线性电感的方法。然后给出了利用JA磁滞模型编程实现非线性电感的方法。最后通过FORTRAN语言在PSCAD中搭建三绕组自耦变压器模型。仿真结果验证了所建模型能够准确地反映自耦变压器的非线性特性。     

Static synchronous series compensator—design,control and application

The design, modeling and control design of a 48-step inverter based static synchronous series compensator (SSSC) is presented in this paper. A magnetic circuit is chosen which contains 18 single-phase three winding transformers and six single-phase two winding transformers to add the output voltages of eight 3-phase inverters. An equivalent circuit model of the SSSC is derived and based on this model a proportional-plus-integral controller is proposed. The SSSC and its control design are then validated through PSCAD/EMTDC simulation of a sample system. The system chosen for the study is the IEEE first benchmark model for subsynchronous resonance (SSR) analysis. It has been shown that the system operates satisfactorily without any SSR for balanced and unbalanced faults.     

基于轴对称模型的特高压变压器直流偏磁分析

文中针对特高压自耦变压器三维模型直流偏磁计算耗时长的问题,通过分析特高压变压器的磁路结构特点,建立了特高压变压器的等效轴对称二维模型,有效减小直流偏磁计算规模。与三维模型进行对比,验证了轴对称模型的正确性和有效性。轴对称模型能够在较短的时间内完成偏磁计算,有效减少直流偏磁的计算工作量,且计算精度可以保证,相较于三维模型有一定优势。在轴对称仿真模型的基础上,进一步分析串联电阻及时间步长对直流偏磁计算精度的影响,并获得了串联电阻的取值范围。最后,通过时域场路耦合原理进行不同直流电流下的特高压变压器负载直流偏磁求解,分析直流偏磁的电磁效应。结果表明,随着直流偏磁电流的增加,励磁电流及绕组电流波形发生严重畸变,并产生很大的谐波分量,影响变压器乃至电力系统的安全稳定运行。     

The ANSI 49 Rectifier with Phase Shift

The ANSI 49 rectifier circuit given in the ANSI Standard C34.2-1968, Section 4 is a single-way three-phase input rectifier that has 120°rectifier conduction, six-pulse output, and does not use an interphase transformer. It is a very desirable circuit but has not been used extensively. Part of the reason for this is the need for separate phase shift transformers to cancel the source. harmonic currents when several of the rectifiers are used together. The ANSI 49 circuit, has a wye primary, six-phase star secondary, and is wound on three single-phase cores or the magnetic equivalent A modification of this circuit is described in which the wye primary is replaced with a partial zig-zag winding, where the zig. and zag windings have unequal turns. By selecting proper ratio of turns of the zig to zag winding, any desired phase shift can be secured. The new circuit is analyzed to show how it works, and test results of a laboratory model are described which fully verify that the circuit operates as theory predicts.     

Parallel operation of three-phase power transformers with different short-circuit voltages

Parallel operation of three-phase power transformers with different short-circuit voltages has been studied using a lab bench. The circuit diagram of the bench and experimentally measured vector diagrams of the currents in primary and secondary windings of the transformers have been presented. It has been found that, when the difference of short-circuit voltages of parallel operating transformers is more than 10%, both an arithmetic difference of currents and a great phase shift of secondary-phase voltages occur. As a result, one of the transformers becomes overloaded, while the other is underloaded. It has experimentally been found that the load current is determined by the geometrical sum of currents of secondary windings in transformers. It has been shown that one of the studied transformers works in the conversion mode and its currents are shifted by 180° with respect to the phase, which is the main reason for failure of the normal operational conditions of parallel transformers.     

一次侧线圈阵列的无线电能传输系统设计

无线电能传输系统采用松耦合变压器进行能量传递,但由于发送端与接收端相对位置较远,耦合系数较低,故带来磁路环节传输效率低的问题。根据松耦合变压器的互感模型,分析了几种因素对传输效率的影响,并选择一次侧和二次侧电路均串联电容的补偿方式,设计了带有两个一次侧线圈的无线电能传输系统,包括一次侧线圈切换电路、电流检测电路以及控制程序。该设计提升了整个系统的功率因数,有效地改善了磁路环节的传输效率。     

Reactive power demand of transformers with DC bias

It has been observed that the presence of DC bias currents/fluxes in power transformers generates harmonic currents and voltages with an associated increase in reactive power (kVAr) demand resulting in a voltage drop. Such DC biases can occur: in transformers near high-voltage DC (HVDC) terminals; due to imperfect or half-controlled rectification resulting in DC, even and odd harmonics; because of geomagnetically induced currents; as a consequence of nuclear explosions changing the Earth's magnetic field; and due to rectifiers working in a normal (e.g., half-wave) mode. The actual network conditions causing such kVAr demand and its suppression, canceling, or mitigation are not very well understood, particularly for transformers with three legs. This article explains for the first time this kVAr demand and its suppression based on experimental data. Tests were performed for three-phase power transformers with three legs, with or without the influence of a magnetic tank     

The Circle Diagram as a Teaching Tool

In today's electrical engineering curriculum, the use of the circle diagram as a teaching and analytical tool is all but forgotten. It has been neglected by the majority of recent textbooks on electromagnetic devices and electric circuits. Yet there are electrical devices whose behavior can easily be understood and analyzed by the use of circle diagrams. In fact, in some cases the use of circle diagrams makes the solution almost a trivial exercise. The graphical and constructional procedures of circle diagrams are presented, and then the circle diagram is employed to analyze two problems: 1) the variation of the mutual and net coil fluxes of a two-winding transformer with varying secondary load impedance, and 2) the study of the variation of the secondary and load voltages of an autotransformer whose load varies from open to short circuit.     

双转子反向对转永磁同步电动机建模与仿真

双转子反向对转永磁同步电动机的两侧要形成反向对转的磁场,就要绕组三相反向排布。由于可以将它看成是两个永磁同步电动机反向串联,所以其电磁路的模型是两个永磁同步电动机模型的合成,但不是简单的合成。定子磁轭磁路为共用,会出现两侧同向和异向并联及串联形式;电路为共用电流形式;会导致该电机先天性的三相不对称,但可以通过优化设计使得三相不对称情况得到很好的解决。     

电磁永磁互调解锁装置仿真与设计

针对工业系统中机械连接的控制需求,设计一种以电磁体和永磁体间的斥力为解锁分离力,永磁体对电磁体铁芯的磁力作为预紧力的电磁永磁互调解锁装置.首先用磁路分析法分析电磁力与永磁力之间的互调原理,然后利用仿真软件分析轭铁关键结构参数对解锁分离力的影响,最后依据研究结论制备了尺寸为45mm×40 mm×40 mm的样机,证明了该...     

磁路结构及材料参数对磁流变抛光区磁场的影响

针对磁流变抛光设备中磁路的结构特点,利用简化的二维模型,基于有限元软件ANSYS,分析了磁路相关参数对抛光区域磁感应强度和分布的影响,具体包括磁路所用导磁材料的磁导率、饱和磁感应强度、气隙长度、磁轭截面积、磁极形状和线圈冷却结构等因素。结果表明,对类似结构的磁路设计,应参考以下几条原则:选用磁导率和饱和磁感应强度高的材料,气隙长度对磁感应强度与分布均有影响,而磁轭截面只需保证材料工作在高导磁线性区即可,磁极形状和线圈冷却结构对抛光区域磁感应强度影响可忽略。     

500kV主变压器中性点加装小电抗器限制短路电流的研究

以东莞电网3个500kV变电站为例,分析500kV变电站220kV侧母线单相短路电流普遍超标的主要原因,提出限制单相短路电流的措施。针对自耦变压器中性点经小电抗器接地方式,阐释小电抗器的电抗值与单相短路电流的关系以及小电抗器对继电保护的影响,从节省投资、简化电路结构的角度推荐采用变压器中性点与小电抗器之间不安装隔离开关的电气主接线方案。东莞电网500kV变电站500kV自耦变压器采用中性点经小电抗器接地方式后,限制220kV侧母线单相短路电流效果明显,增强了变电站短路电流水平对电网建设的适应性。     

500kV变压器直流偏磁下的铁心损耗分析研究

为了研究变压器直流偏磁下的铁心损耗,文章以某一核电站500 k V主变压器为例,在二维有限元瞬态场A–φ算法基础下构造了直流偏磁下的变压器二维仿真损耗模型。在仿真中,偏磁直流量从0 A增加至30 A,可得到变压器铁心的损耗分布。结果分析可表明:随着偏磁直流量的增加,励磁电流会产生畸变和较大的偶次谐波,并导致铁心局部损耗增大,其中:铁心主柱与上、下铁轭交接区域的损耗值受到直流偏磁的影响最大,铁心水平路径的损耗值相较于垂直路径受直流偏磁的影响较大。     

特高压自耦变压器的建模和电磁暂态仿真

为了在特高压环境下正确应用变压器差动保护,需要对特高压变压器进行合理建模,并进行相应的电磁暂态仿真。根据三绕组自耦变压器星型等值电路的原理,用电磁暂态仿真软件EMTDC中的统一电磁等效电路(unified magnetic equivalent circuit,UMEC)普通三绕组变压器模型来模拟1000MVA/1050kV三绕组自耦变压器,将特高压变压器参数折算成UMEC模型参数,形成特高压变压器模型。在特高压环境下,分别进行励磁涌流和故障电流仿真,并用于考察应用得最为广泛的2次谐波闭锁的变压器差动保护的动作可靠性。分析表明:当合闸角和剩磁满足一定条件时,特高压变压器三相励磁涌流的2次谐波含量都会在10%以下,即使采用一相制动三相的2次谐波闭锁策略,如果2次谐波门槛值维持在15%～20%,也不能避免差动保护误动;另外,在某些轻微故障的情况下,故障初期故障电流的2次谐波含量成分较高,会使保护动作短暂延迟。